Air injection nozzle, and tenter oven using the nozzle

ABSTRACT

An air injection nozzle has an air injection face with a number of air injection holes arrayed at an interval (Py) in first and second staggered rows. The first row and the second rows are positioned at an interval (Px). The air injection face and the sheet running face confront each other at a distance (L). The air injection holes in the air injection face have a diameter (D). The interval (Px), the interval (Py), the distance (L) and the diameter (D) satisfy Formula (1): 6≰(L/D)/(Px/Py)≰9, and Formula (2): 4≰L/D≰8. This air injection nozzle is employed as a resin film heat treating apparatus in a tenter oven to be used for manufacturing the resin film.

TECHNICAL FIELD

The present invention relates to an air ejection nozzle used forheating, cooling or heat-retaining a resin film and a tenter oven usingthe same.

BACKGROUND ART

Known methods for producing a biaxially oriented resin film such as abiaxially oriented polyester film include a sequential biaxialstretching method comprising the steps of continuously discharging aflowable resin from a die as a sheet, cooling and solidifying thedischarged sheet on a casting drum, to form a cast film, stretching theformed cast film in the carrying direction of the film, namely, in themachine direction using a longitudinal stretching machine andsubsequently stretching the film stretched in the machine direction(monoaxially oriented film) in the width direction of the film(transverse direction) in a tenter oven, and a simultaneous biaxialstretching method of stretching the cast film in the carrying directionof the film (machine direction) and in the width direction of the film(transverse direction) in a tenter oven.

In the tenter oven used for these production methods, installed are airejection nozzles having many air ejection holes formed in the surfacesthereof to face a surface of a resin film passing through the tenteroven. Usually, multiple air ejection nozzles are installed at regularintervals in the resin film carrying direction in such a manner that thelongitudinal direction of the air ejection nozzles is kept perpendicularto the resin film carrying direction.

The air ejection nozzles are provided in a nozzle housing. The nozzlehousing has an air supply passage therein and has an air ejection faceas one of the surfaces thereof. The ends on one side of the many airejection holes are opened in the air ejection face, and the ends on theother side are opened into the air supply passage. To another surface orother two surfaces of the nozzle housing, an air supply duct isconnected, and one end of the air supply duct communicates with the airsupply passage in the nozzle housing while the other end is connectedwith a heat exchanger and a fan. The air controlled to a desiredtemperature by the heat exchanger is sent by the fan to the respectiveair ejection holes through the air supply duct and the air supplypassage in the nozzle housing, and is ejected toward the surface of theresin film from the respective air ejection holes open in the airejection face of the housing. The ejected air is usually collected fromsuction ports formed in the tenter oven, to be reused.

In general, the tenter oven has multiple divisional zones such as apreheating zone, stretching zone, heat setting zone and cooling zone inthe resin film carrying direction. The tenter oven has such a structurethat the temperatures of the air used in the respective zones can be setindependently for the respective zones. The tenter oven is provided withnumerous clips outside both the edges of the resin film for holding theedges of the resin film moving along rails from the inlet portion towardthe outlet portion of the tenter oven.

In the tenter oven, the resin film held at both the edges thereof andcarried by the clips is heated in the preheating zone to a temperaturesuitable for stretching, and stretched at least in the transversedirection in the stretching zone, then being heat-treated in the heatsetting zone, cooling zone, etc. The air ejection nozzles are used toeject the air controlled at a desired temperature toward the surface ofthe resin film, for promoting the heat exchange between the air and theresin film, to thereby heat, cool or heat-retain the resin film.

The properties of the resin film produced like this are affected by theheat history which the resin film encounters while it passes through therespective zones of the tenter oven. Therefore, to obtain a resin filmhaving uniform properties in the width direction of the resin film, itis important that the heat exchange between the air ejected from the airejection nozzles and the resin film takes place uniformly in the widthdirection of the resin film. For this purpose, the air ejection nozzlesare required to assure that the temperature of the air striking theresin film is uniform in the width direction of the resin film and thatthe heat transfer efficiency of the air ejection nozzles is uniform inthe width direction of the resin film.

An air ejection nozzle having a continuous air ejection hole formed inthe width direction of the resin film on the surface thereof facing thesurface of the resin film is called a slit nozzle. As a conventionalslit nozzle for the purpose of keeping the ejection velocity andtemperature of air uniform in the width direction of the resin film, anozzle having a duct of countercurrent flow design is proposed (seePatent Literature 1). However, a slit nozzle has a problem that the airjet is liable to bend in the progress direction. If the air jet bends inthe progress direction, air masses different in temperature are mixed ata portion where zones different in set temperature contact each other,and large temperature irregularity can occur in the width direction ofthe resin film. In this case, it is difficult to obtain a resin filmhaving uniform properties in the width direction.

According to the finding by the present inventors, the abovementionedproblem that the air jet is liable to bend in the progress direction canbe improved by arranging air ejection holes discretely in the widthdirection of the resin film, that is, by arranging many air ejectionholes independent of each other at regular intervals. The reason isconsidered to be that the air jets finely divided in the width directionof the resin film form air passing portions between the respectivelyadjacent air jets, such that the air existing in the front and back ofthe air ejection nozzle can be guided to pass through the air passingportions, to ease the difference of the pressures in the front and backof the air ejection nozzle. As such an air ejection nozzle, there is ahole nozzle having many circular air ejection holes in the face thereoffacing the surface of the resin film. However, if many air ejectionholes are arranged at regular intervals in the width direction of theresin film, the heat transfer rate of the surface of the resin filmbecomes uneven in the width direction of the resin film, to raise aproblem that the uniformity of heat transfer efficiency declines.

Proposed is a conventional hole nozzle for the purpose of enhancing theheat transfer rate of the surface of the resin film, in which while thedistance between the air ejection holes and the surface of the resinfilm is set at 4 to 6 times the diameter of the air injection holes,many such air ejection holes are arranged zigzag in six rows in thedirection perpendicular to the resin film carrying direction (see PatentLiterature 2). However, the magnitude of heat transfer rate and theuniformity of heat transfer efficiency in the width direction of theresin film are different problems, and it is difficult to improve theuniformity of heat transfer efficiency in the width direction of theresin film only by discussing the diameter of air ejection holes and thenumber of rows of air ejection holes.

The conventional hole nozzles intended to improve the uniformity of heattransfer efficiency in the width direction of the resin film include ahole nozzle used as a device for cooling the resin film on a castingdrum (see Patent Literature 3) and a hole nozzle used as a drying deviceof a printing machine or coating machine (see Patent Literature 4).However, these hole nozzles are effective in the case where the distancebetween the air ejection holes and the surface of the resin film is madeshorter than 20 mm, and it is not preferred to use such hole nozzles ina tenter oven in which the distance between the air ejection holes andthe surface of the resin film is generally 140 to 270 mm, since the heattransfer rate of the surface of the resin film may decline remarkably.

Patent Literature 1: JP 1634915 B

Patent Literature 2: JU 2528669 B

Patent Literature 3 JP 3374527 B

Patent Literature 4: JU 2008679 B

SUMMARY OF INVENTION Technical Problem

One object of the invention is to solve the problems of theabovementioned prior art by providing an air injection nozzle good inthe uniformity of heat transfer efficiency in the width direction of theresin film. Another object of the invention is to provide a tenter ovengood in the uniformity of heat transfer efficiency in the widthdirection of the resin film using the air ejection nozzle of theinvention.

Solution to Problem

An air ejection nozzle of the invention comprises:

(a) an air ejection nozzle which is provided against a passing plane ofa resin film carrying one direction with a clearance and used forejecting air toward a surface of the resin film, wherein

(b) the air ejection nozzle comprises a nozzle housing, and the nozzlehousing has an air supply passage therein, an air ejection face facingthe passing plane of the resin film, and many air ejection holes openingto the air supply passage and opening in the air ejection facerespectively,

(c) a figure of each of openings of the many air ejection holes in theair ejection face is circle,

(d) the many air ejection holes are arranged in the air ejection face intwo rows of a first row and a second row in the direction perpendicularto the carrying direction of the resin film, and a state of arrangementbetween the air ejection holes of the first row and the air ejectionholes of the second row is a zigzag arrangement, and

(e) the distance L (mm) between the air ejection face and the passingplane of the resin film, the diameter D (mm) of the respective airejection holes in the air ejection face, the interval Px (mm) in thecarrying direction of the resin film between a first air ejectionholes-aligned straight line passing through the centers of the multipleair ejection holes arranged in the first row and a second air ejectionholes-aligned straight line passing through the centers of the multipleair ejection holes arranged in the second row, and each interval Py (mm)between the centers of the respectively adjacent air ejection holes inthe first air ejection holes-aligned straight line and between thecenters of the respectively adjacent air ejection holes in the secondair ejection holes-aligned straight line satisfy the following formulae(1) and (2):6≦(L/D)/(Px/Py)≦9  formula (1)4≦L/D≦8  formula (2)

In the air ejection nozzle of the invention, it is preferred that thefollowing formula (3) is satisfied:12≦L/B≦30  formula (3)

where B=2π(D/2)²/Py (where π is the ratio of the circumference of acircle to its diameter).

In the air ejection nozzle of the invention, it is preferred that thedistance L is 140 to 270 mm.

A tenter oven of the invention comprising:

(a) an oven housing having an inlet of a resin film at one end thereofand an outlet of the resin film at the other end thereof,

(b) having a stretching zone between the inlet of the resin film and theoutlet of the resin film, for stretching the resin film at least in thedirection perpendicular to the carrying direction of the resin filmwhile the resin film is carried from the inlet of the resin film towardthe outlet of the resin film, and

(c) having a heat treatment zone between the inlet of the resin film andthe outlet of the resin film, for ejecting air toward a surface of theresin film and heat treating the resin film, wherein

(d) the air ejection face of the air ejection nozzle of the invention ispositioned to face a passing plane of the resin film formed between theinlet of the resin film and the outlet of the resin film, and

(e) the air ejection nozzle is provided in the heat treatment zone insuch a manner that the directions of the first row and the second row ofthe air ejection holes of the air ejection nozzle are kept perpendicularto the carrying direction of the resin film.

In the tenter oven of the invention, it is preferred that the heattreatment zone includes a preheating zone, a stretching zone, a heatsetting zone and a cooling zone in the order from the inlet of the resinfilm toward the outlet of the resin film, and the air ejection nozzle isprovided at least in one of these zones.

In the tenter oven of the invention, the stretching zone may be asimultaneously biaxial stretching zone in which the resin film isstretched in the direction perpendicular to the carrying direction ofthe resin film and stretched in the carrying direction of the resinfilm.

In the tenter oven of the invention, it is preferred that the airejection nozzle is provided on both sides of the passing plane of theresin film having a clearance formed against the passing plane of theresin film.

Advantageous Effects Invention

The air ejection nozzle of the invention has many air ejection holeshaving specific forms and arranged in a specific positionalrelationship. Therefore, if the air ejection nozzle is used forheat-treating a resin film, excellent uniformity of heat transferefficiency in the width direction of the resin film can be obtained.Therefore, the tenter oven of the invention using the air ejectionnozzle of the invention allows a production of a resin film havinghomogeneous heat-treated properties in the width direction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an enlarged plan view showing a portion of the air ejectionface of an air ejection nozzle of the invention shown in FIG. 2.

FIG. 2 is a perspective view showing an example of the air ejectionnozzle of the invention.

FIG. 3 is a plan view for explaining an example of the heat transferrate distribution on a surface of a resin film.

FIG. 4 is a plan view (top view) for explaining an example of a tenterapparatus.

FIG. 5 is the C1-C1 sectional view of FIG. 4 in arrow direction.

FIG. 6 is the C2-C2 sectional view of FIG. 5 in arrow direction.

FIG. 7 is a schematic process chart for explaining an example of a resinfilm production process using a sequential biaxial stretching method.

FIG. 8 is a sectional view of an analysis model for explaining anexample of the analysis model used for calculating the heat transferrate distribution on a surface of a resin film.

FIG. 9 is a chart for explaining the heat transfer efficiencydistribution of an air ejection nozzle in the width direction of a resinfilm.

FIG. 10 is a graph obtained by plotting the values of (L/D)/(Px/Py) andthe values of heat transfer efficiency irregularity Rp obtained inexamples and comparative examples of the invention.

FIG. 11 is a graph obtained by plotting the values of Px/Py and thevalues of L/D obtained in examples and comparative examples of theinvention.

FIG. 12 is a graph showing the thickness distribution in the widthdirection of the resin film in Example 16 of the invention.

FIG. 13 is a graph showing the thickness distribution in the widthdirection of the resin film in Comparative Example 18 of the invention.

Reference Signs List  1 air ejection nozzle  1A upper air ejectionnozzle  1Af, 1Bf air ejection face  1a nozzle housing  1B lower airejection nozzle  2, 2A, 2B air ejection hole  2a first row in thearrangement of air ejection holes  2b second row in the arrangement ofair ejection holes  3a straight line passing through the centers of theair ejection holes arranged in first row (first air ejectionholes-aligned straight line)  3b straight line passing through thecenters of the air ejection holes arranged in second row (second airejection holes-aligned straight line)  4a center line between airejection nozzle 1 and air ejection nozzle 11a adjacent to the airejection nozzle 1 on the upstream side in the resin film carryingdirection  4b center line between air ejection nozzle 1 and air ejectionnozzle 11b adjacent to the air ejection nozzle 1 on the downstream sidein the resin film carrying direction  5a straight line passing throughthe centers of the air ejection holes arranged in the first row 2a anddrawn in the resin film carrying direction  5b straight line passingthrough the center between straight line 5a and straight line 5c  5cstraight line passing through the centers of the air ejection holesarranged in the second row 2b and drawn in the resin film carryingdirection 11a, 11b air injection nozzle adjacent to air ejection nozzle1 20 air ejection plate 21 opening of air ejection hole 31 resin film31a resin sheet 31b non-oriented film 31c monoaxially oriented film 31bbiaxially oriented film 31e film as a product 33 heat transfer ratedistribution on a surface of a resin film 40, 40A air ejection face 41air supply passage 41a, 41b air introducing port 51 tenter oven 51A ovenhousing 51a inlet of resin film 51b outlet of resin film 52A, 52B heatexchanger 53A, 53B fan 54 suction duct 54A, 54B suction port 61 outsidespace of tenter oven 62 end boundary of analysis space 71A, 71B rail73A, 73B clip 91 extruder 92 die 93 casting drum 94 longitudinalstretching machine 95 tenter apparatus 96 winding roll 511 preheatingzone 512 stretching zone 523 heat setting zone 514 cooling zone Ddiameter of air ejection hole (opening of air ejection hole in airejection face) FTD carrying direction of a resin film FPf passing planeof a resin film HTC magnitude indicator of heat transfer rate HTCLportion of large heat transfer rate HTCS portion of small heat transferrate L distance between the air ejection face where air ejection holesare arranged and the passing plane of a resin film Pn section betweencenter line 4a and center line 4b Px interval between straight line 3aand straight line 3b Py interval between the centers of respectivelyadjacent air ejection holes in the respective rows of first row 2a andsecond row 2b Q heat transfer efficiency of air ejection nozzle Qaaverage heat transfer efficiency of air ejection nozzle Qmax maximumvalue of heat transfer efficiency of air ejection nozzle Qmin minimumvalue of heat transfer efficiency of air ejection nozzle Rq heattransfer efficiency irregularity of air ejection nozzle in the widthdirection of a resin film Rt thickness irregularity in the widthdirection of a resin film Ta average value of thickness distributed inthe width direction of a resin film Tn minimum value of thicknessdistributed in the width direction of a resin film Tx maximum value ofthickness distributed in the width direction of a resin film

DESCRIPTION OF EMBODIMENTS

Known methods for producing a resin film include a melt film formationmethod and a solution film formation method. In these film formationmethods, a molten resin or a resin solution is continuously extrudedfrom a slit opening of a die, to form a cast sheet-like resin film. Theobtained cast resin film is then stretched in the machine directionand/or in the transverse direction.

Below is explained an example in reference to drawings, in which an airejection nozzle and a tenter oven of the invention are applied to aprocess for producing a biaxially oriented resin film to be obtained bystretching a cast resin film formed by the aforementioned melt filmformation method in the machine direction and in the transversedirection.

FIG. 7 is a schematic process chart showing an example of a resin filmproduction process using a sequential biaxial stretching method. In thesequential biaxial stretching method, a cast resin film is stretched atfirst in the machine direction, to obtain a monoaxially oriented resinfilm, and the obtained monoaxially oriented resin film is stretched inthe transverse direction.

The resin film production process using a sequential biaxial stretchingmethod is, as shown in FIG. 7, provided with an extruder 91, die 92,casting drum 93, longitudinal stretching machine 94, tenter apparatus 95and winding roll 96.

A resin polymer is melted in the extruder 91 and extruded toward the die92, being discharged as a sheet from the die 92. The resin sheet 31 adischarged from the die 92 is cooled and solidified by the casting drum93, to obtain a cast film 31 b. Then, the cast film 31 b is stretched bythe longitudinal stretching machine 94 in the machine direction, namely,in the carrying direction, to obtain a monoaxially oriented film 31 c.The obtained monoaxially oriented film 31 c is stretched in the tenterapparatus 95 in the transverse direction, to obtain a biaxially orientedfilm 31 d. Subsequently, the biaxially oriented film 31 d iscontinuously wound around the winding roll 96, to obtain a film 31 e asa rolled product. Hereinafter, the cast film 31 b, monoaxially orientedfilm 31 c or biaxially stretched film 31 d may be called simply as aresin film 31.

In the case where a surface of the film as a product is required to bemodified, the film may be coated on the surface with a desired coatingliquid as the case may be. When the film is coated, the monoaxiallystretched film 31 c is coated on the surface immediately before thetenter apparatus 95 in the production process shown in FIG. 7.

A case of using a sequential biaxial stretching method has beenexplained. In the case where a simultaneous biaxial stretching method isused, the longitudinal stretching machine 94 is not used, and the castfilm 31 b cooled and solidified by the casting drum 93 is stretched inthe tenter apparatus 95 simultaneously in the longitudinal direction(carrying direction) of the resin film and the width direction of theresin film, to obtain a biaxially oriented film.

The carrying direction of the resin film refers to the direction inwhich the continuous resin film runs continuously, namely, thelongitudinal direction of the continuously running resin film, and inthe production process of FIG. 7, the carrying direction refers to thedirection in which the resin film runs from the extruder 91 toward thewinding roll 96.

FIG. 4 is a plan view (top view) showing an example of the tenterapparatus 95 shown in FIG. 7. In FIG. 4, the tenter apparatus 95 hasrail 71A and rail 71B disposed in opposite to each other, numerous clips73A and 73B running along the rails 71A and 71B, and a tenter oven 51for ejecting the air controlled to a desired temperature to a surface ofthe rein film and collecting the ejected air for recycled use. Thedirection in which the resin film 31 is carried in the tenter oven 51 isindicated by arrow FTD. The tenter oven 51 comprises an oven housing51A, and the oven housing 51A has a resin film inlet 51 a at one endthereof and a resin film outlet 51 b at the other end thereof.

The clips 73A and 73B hold both the edges of the resin film 31 at theresin film inlet 51 a and pass through the tenter oven 51, releasing theresin film 31 at the resin film outlet 51 b.

The tenter oven 51 has at least a stretching zone between the resin filminlet 51 a and the resin film outlet 51 b for stretching the resin film31 in the direction perpendicular to the carrying direction FTD of theresin film 31 while the resin film 31 is carried from the resin filminlet 51 a to the resin film outlet 51 b. Further, the tenter oven 51has heat treatment zones between the resin film inlet 51 a and the resinfilm outlet 51 b for ejecting air toward a surface of the resin film 31for heat-treating the resin film.

In this example, the tenter oven 51 has four heat treatment zonesincluding a preheating zone 511, a stretching zone 512, a heat settingzone 513 and a cooling zone 514 in the order from the upstream side tothe downstream side in the carrying direction FTD of the resin film 31,and desired air temperatures can be set in the respective zones.

Each of the zones may also be further divided into multiple chambers inthe carrying direction FTD of the resin film 31, so that the temperatureof air can be set differently in the respective chambers. That is, thetenter oven 51 can also be constituted, for example, such that thepreheating zone 511 has three chambers, that the stretching zone 512 hasfour chambers, that the heat setting zone 513 has two chambers and thatthe cooling zone 514 has one chamber. In this case, the temperatures ofthe respective chambers of each zone can also be independently set.

With regard to the air temperature ranges of the respective zones, inthe case where the resin film 31 is, for example, a polyester film, itis preferred that the temperature of the preheating zone 511 is 80 to140° C., that the temperature of the stretching zone 512 is 80 to 200°C., that the temperature of the heat setting zone 513 is 150 to 240° C.and that the cooling zone 514 is 50 to 200° C.

If the rails 71A and 71B are installed to be gradually wider in therelative distance between the rail 71A and the rail 71B (the gaugebetween the rail 71A and the rail 71B in the direction perpendicular tothe carrying direction FTD of the resin film 31) in the stretching zone512, the resin film 31 can be stretched in the width direction thereof(the direction perpendicular to the carrying direction FTD of the resinfilm 31). As required, if a section in which the relative distancebetween the rail 71A and the rail 71B becomes gradually narrow isestablished in the heat setting zone 513 or in the cooling zone 514, theresin film 31 can be treated to be relaxed in the width directionthereof.

In the case where a simultaneous biaxial stretching method is employed,in the stretching zone 512 of the tenter oven 51, the intervals betweenthe respective clips 73A and the intervals between the respective clips73B respectively running along the rails 71A and 71B are graduallywidened. As a result, the resin film 31 can be stretched also in thecarrying direction FTD, to allow simultaneous biaxial stretching.

FIG. 5 is the C1-C1 sectional view of FIG. 4 in the arrow direction.FIG. 6 is the C2-C2 sectional view of FIG. 5 in the arrow direction. Thetenter oven 51 shown in FIG. 4 has multiple upper air ejection nozzles1A installed at intervals in the carrying direction FTD of the resinfilm 31, to face the upper surface of the resin film 31 as shown in FIG.5, and further has multiple lower air ejection nozzles 1B installed atintervals in the carrying direction FTD of the resin film 31, to facethe lower surface of the resin film 31. In the heat setting zone 513 ofFIG. 5, six upper air ejection nozzles and six lower air ejectionnozzles are shown. As shown in FIG. 6, the respective upper air ejectionnozzles 1A and the respective lower air ejection nozzles 1B areinstalled to extend in the width direction of the resin film 31 (thedirection perpendicular to the carrying direction FTD).

On the top surface of the oven housing 51A of the tenter oven 51, heatexchangers 52A and 52B are installed. The air controlled to a desiredtemperature by the heat exchangers 52A and 52B is sent by fans 53A and53B into the respective air ejection nozzles 1A and 1B, and dischargedfrom the air ejection holes 2A and 2B formed in the faces (air ejectionfaces) 1Af and 1Bf of the air ejection nozzles 1A and 1B facing thesurfaces of the resin film 31. The discharged air passes through thesuction ports 54A and 54B in the tenter oven 51 and is collected intothe heat exchangers 52A and 52B. The collected air is used in recycle inthe tenter oven 51. Meanwhile, FIG. 5 shows the portion of the heatsetting zone 513 in the tenter oven 51 of the tenter apparatus 95, butthe same structure can be used also in other zones of the tenter oven 51such as the preheating zone 511, stretching zone 512 and cooling zone514.

The air ejection nozzle ejects air controlled at a desired temperaturetoward a surface of the resin film carried in one direction, acting topromote heat exchange between the air and the resin film. That is, inthe case where the temperature of the resin film is lower than thetemperature of the air ejected from the air ejection nozzle toward thesurface of the resin film, the resin film is heated, and in the casewhere the temperature of the resin film is higher than the temperatureof the air ejected from the air ejection nozzle toward the surface ofthe resin film, the resin film is cooled. Further, in the case where thetemperature of the resin film is equal to the temperature of the airejected from the air ejection nozzle toward the surface of the resinfilm, the resin film is heat-retained. Moreover, in the case where theresin film is coated on the surface with a coating liquid immediatelybefore the tenter apparatus 95, the formed coating film is dried orcured by the heat exchange with the air ejected from the air ejectionnozzle to the surface of the coating film.

The number of the air ejection nozzles in the resin film carryingdirection can also be one in each zone, but considering the efficiencyof heat exchange between the air and the resin film, it is preferredthat at least three air ejection nozzles are used. Further, the airejection nozzle can also be installed on one surface side only of theresin film, but considering the efficiency of heat exchange between theair and the resin film, it is preferred that the air ejection nozzlesare installed on both the surface sides of the resin film.

FIG. 2 is a perspective view showing an example of the air ejectionnozzle of this invention. In FIG. 2, the air ejection nozzle 1 comprisesa nozzle housing 1 a. The nozzle housing 1 a has air introducing ports41 a and 41 b for introducing air having a predetermined temperatureinto the nozzle housing 1 a at both the ends thereof in the longitudinaldirection, and the inside space between the air introducing port 41 aand the air introducing port 41 b forms an air supply passage 41.

Further, the nozzle housing 1 a is mounted with an air ejection plate 20on the top surface opening of the housing. The air ejection plate 20 hasmany air ejection holes 2 open on one side in the outside surface of theair ejection plate 20 and open on the other side in the inside surfaceof the air ejection plate 20, namely, open into the air supply passage41. Therefore, the outside surface of the air ejection plate 20 forms anair ejection face 40 having many openings 21 of the air ejection holes2. The air ejection nozzle 1 is used in such a manner that the airejection face 40 thereof faces the surface of the resin film to beheat-treated, with a clearance formed between them.

FIG. 1 is an enlarged plan view showing a portion of the air ejectionface 40 of the air ejection nozzle 1 of the invention shown in FIG. 2.In FIG. 1, the air ejection nozzle 1 has many air ejection holes 2 withopenings 21 in the face of the air ejection nozzle 1 facing the surfaceof the resin film, namely, in the air ejection face 40. The form of therespective air ejection holes in the air ejection face 40, namely, theform of the respective openings 21 is circular. The diameter of therespective air ejection holes 2 in the air ejection face 40, namely, thediameter of the respective openings 21 is D (mm).

The many air ejection holes 2, namely, the many openings 21 are arrangedin two rows consisting of the first row 2 a and the second row 2 b inthe air ejection face 40. The direction of the first row 2 a and thesecond row 2 b is the direction perpendicular to the resin film carryingdirection FTD (the width direction of the resin film). The first row 2 ais positioned on the upstream side in the resin film carrying directionFTD, and the second row 2 b is positioned on the downstream side in theresin film carrying direction FTD. The air ejection holes 2 arranged inthe first row 2 a and the air ejection holes 2 arranged in the secondrow 2 b are arranged zigzag in the plan view.

In FIG. 1, the interval between a straight line 3 a (a first airejection holes-aligned straight line) passing through the centers of theair ejection holes 2 arranged in the first row 2 a and a straight line 3b (a second air ejection holes-aligned straight line) passing throughthe centers of the air ejection holes 2 arranged in the second row 2 bin the resin film carrying direction FTD is expressed as Px (mm).Further, each interval between the centers of the respectively adjacentair ejection holes 2 in the first row 2 a and between the centers of therespectively adjacent air ejection holes 2 in the second row 2 b isexpressed as Py (mm).

In the abovementioned zigzag arrangement, it is preferred that thecenter of each air ejection hole 2 of the first row 2 a shifts from thecenter of the air ejection hole 2 of the second row 2 b nearest to theair ejection hole of the first row by Py/2 in the width direction of theresin film. However, the interval Py/2 between each air ejection hole ofthe first row and the air ejection hole of the second row nearest to theair ejection hole of the first row can also be a value within a range ofPy/2±10%.

FIG. 3 is a plan view showing a state of the heat transfer ratedistribution 33 on a surface of a resin film obtained by the numericalanalysis explained for the examples described later. The heat transferrate in the heat transfer rate distribution 33 is largest at the centralposition of each air ejection hole 2 of the air ejection nozzle 1 andbecomes smaller at a position farther away from the central position ofthe air ejection hole 2. The heat transfer efficiency of one airejection nozzle 1 is the mean value of the heat transfer rates in thecarrying direction FTD of the resin film 31 in a section Pn ranging fromthe center line 4 a between the air ejection nozzle 1 and the airejection nozzle 11 a adjacent to the air ejection nozzle 1 on theupstream side in the resin film carrying direction to the center line 4b between the air ejection nozzle 1 and the air ejection nozzle 11 badjacent to the air ejection nozzle 1 on the downstream side in theresin film carrying direction. The center lines 4 a and 4 b, thestraight line 3 a (the first air ejection holes-aligned straight line)passing through the centers of the air ejection holes 2 of the first row2 a and the straight line 3 b (the second air ejection holes-alignedstraight line) passing through the centers of the air ejection holes 2of the second row 2 b are parallel to each other.

Straight lines 5 a, 5 b and 5 c drawn in the resin film carryingdirection FTD in FIG. 3 are explained below.

The straight line 5 a is a line passing through the center of an airejection hole 2 arranged in the first row 2 a and the straight line 5 cis a line passing through the center of an air ejection hole 2 arrangedin the second row 2 b. The straight line 5 b is a line passing throughthe center of the interval between the straight line 5 a and thestraight line 5 c.

Next, the history of the heat transfer rates occurring on the surface ofthe carried and moved resin film at the positions corresponding to theselines is explained below. The heat transfer rate on the surface portionof the resin film passing the position corresponding to the straightline 5 a is large when the surface portion of the film passes over thefirst row 2 a but is small when it passes over the second row 2 b. Thereason is that the straight line 5 a passes the center of an airejection hole 2 on the first row 2 a but a position apart from thecenters of air ejection holes 2 on the second row 2 b, therefore thatwhen the surface portion of the resin film corresponding to the straightline 5 a passes over the first row 2 a, it passes over the air ejectionhole 2, hence the heat transfer rate being large, and that when thesurface portion of the resin film passes over the second row 2 b, itpasses over a position apart from air ejection holes 2, hence the heattransfer rate being small.

The heat transfer rate on the surface portion of the resin filmcorresponding to the straight line 5 c is small when the surface portionof the resin film passes over the first row 2 a, but is large when itpasses over the second row 2 b. Likewise, the straight line 5 c passes aposition apart from air ejection holes 2 when it passes the first row 2a, and therefore when the surface portion of the resin filmcorresponding to the straight line 5 c passes over the first row 2 a,the heat transfer rate on the surface portion of the resin film becomessmall, and when the surface portion of the resin film passes over thesecond row 2 b, the heat transfer rate on the surface portion of theresin film becomes large since the surface portion of the resin filmpasses over the center of an air ejection hole 2 of the second row 2 b.

The heat transfer rate on the surface portion of the resin filmcorresponding to the straight line 5 b becomes medium when the surfaceportion of the resin film passes over the first row 2 a and when itpasses over the second row 2 b. The reason is that when the straightline 5 b passes the first row 2 a, it is farther from an air ejectionhole 2 than the straight line 5 a and closer to an air ejection hole 2than the straight line 5 c, and further that when it passes the secondrow 2 b, it is closer to an air ejection hole 2 than the straight line 5a and is farther away from an air ejection hole than the straight line 5c. The heat transfer efficiency of the air ejection nozzle 1 is the meanvalue of these heat transfer rates experienced.

In FIG. 3, the magnitudes in terms of the heat transfer rates of theresin film 31 are expressed by shades on the surface of the resin film31. FIG. 3 shows indicator HTC for expressing the magnitude in terms ofheat transfer rate. As the indicator HTC, dark HTCL means a portionhaving a large heat transfer rate, and light HTCS means a portion havinga small heat transfer rate. If the color shades in the indicator HTC arecompared with the color shade pattern shown on the surface of the resinfilm 31, the portions having high heat transfer rates and the portionshaving low heat transfer rates on the resin film 31 can be read.

If the air ejection nozzle 1 in which the air ejection holes 2 arearranged zigzag in two rows in the direction perpendicular to the resinfilm carrying direction is used, the heat transfer efficiency in theresin film portion corresponding to the straight line 5 a is almostequal to the heat transfer efficiency in the resin film portioncorresponding to the straight line 5 c, needless to say. The airejection holes arranged like this allow the difference between the heattransfer efficiency in the resin film portions corresponding to thestraight lines 5 a and 5 c, and the heat transfer efficiency in theresin film portion corresponding to the straight line 5 b to bedecreased. Compared with the case where the air ejection holes 2 arearranged in one row only in the resin film carrying direction, theuniformity of heat transfer efficiency in the width direction of theresin film can be improved.

However, even if the air ejection holes 2 are arranged zigzag in tworows in the direction perpendicular to the resin film carryingdirection, the uniformity of heat transfer efficiency is notsatisfactorily enough. For further decreasing the difference between theheat transfer efficiency in the portions corresponding to the straightlines 5 a and 5 c and the heat transfer efficiency in the portioncorresponding to the straight dine 5 b, it is important to select thedimensions of the portions explained below as factors affecting the heattransfer rate distribution 33 in good balance.

It is necessary that the air ejection nozzle 1 of the inventionsatisfies the following formulae (1) and (2), where L (mm) is thedistance between the air ejection holes 2 and the passing plane of theresin film 31; D (mm) is the diameter of the air ejection holes 2 in theair ejection face 40; Px (mm) is the interval between the straight line3 a (the first air ejection holes-aligned straight line) passing throughthe centers of the air ejection holes 2 of the first row 2 a and thestraight line 3 b (the second air ejection holes-aligned straight line)passing through the centers of the air ejection holes 2 of the secondrow 2 b; and Py (mm) is each interval between the centers of therespectively adjacent air ejection holes 2 in each row in the widthdirection of the resin film.6≦(L/D)/(Px/Py)≦9  formula (1)4≦L/D≦8  formula (2)

In the above, the passing plane FPf of the resin film 31 refers to thegeometrical plane passing through the positions where the respectiveclips 73A and 73B existing in the tenter oven 51 hold the resin film 31.

Further, it is preferred that the cross sectional form of the airejection holes 2 is closer to a geometric circle but is not required tobe completely round. Therefore, the diameter D is defined as thediameter of the circle obtained by least square approximation of the airejection holes 2. It is preferred that the circularity tolerance of theair ejection holes 2 is within ±5% of diameter D.

The formula (1) is explained below. If the value of Px/Py as thedenominator of formula (1) is diminished, a state of arrangement of theair ejection holes 2 approaches to a state of arrangement in one rowunder at intervals of Py/2 in the width direction of the resin film 31.Therefore, the heat transfer efficiency of the air ejection nozzle atthe position corresponding to the straight line 5 b declines. On thecontrary, if the value of Px/Py is enlarged, the heat transferefficiency of the air ejection nozzles at the position corresponding tothe straight line 5 b becomes larger than the heat transfer efficiencyof the air ejection nozzle at the positions corresponding to thestraight line 5 a and the straight line 5 c. Therefore, among the valuesof Px/Py, there is a range where the difference between the heattransfer efficiency of the air ejection nozzle at the positionscorresponding to the straight line 5 a and the straight line 5 c and theheat transfer efficiency of the air ejection nozzle at the positioncorresponding to the straight line 5 b becomes small.

The inventors found that the range where the difference between the heattransfer efficiency at the positions corresponding to the straight lines5 a and 5 c and the heat transfer efficiency at the positioncorresponding to the straight line 5 b becomes small depends on thevalue of L/D. That is, if the value of L/D is diminished, the regionwhere the heat transfer rate is large is widened, and the heat transferefficiency of the air ejection nozzle at the position corresponding tothe straight line 5 b becomes smaller than the heat transfer efficiencyof the air ejection nozzle at the positions corresponding to thestraight line 5 a and the straight line 5 c. Therefore, it is preferredthat the value of Px/Py is made smaller. On the contrary, if the valueof L/D is enlarged, the region where the heat transfer rate is large isnarrowed, and the heat transfer efficiency of the air ejection nozzle atthe position corresponding to the straight line 5 b becomes larger thanthe heat transfer efficiency of the air ejection nozzle at the positionscorresponding to the straight line 5 a and the straight line 5 c.Therefore, it is preferred that the value of Px/Py is made larger. Thepreferred relationship between the value of L/D and the value of Px/Pywas discussed by the method shown in the examples, and as a result, itwas found that in the case where the value of (L/D)/(Px/Py) was in arange from 6 to 9, the uniformity of heat transfer efficiency of the airejection nozzle in the width direction of the resin film could begreatly improved.

Further, in the examples, it was found preferred that the value of(L/D)/(Px/Py) was in a range from 6 to 9, but it was found that theuniformity of the heat transfer efficiency of the air ejection nozzle inthe width direction of the resin film could be further improved when thevalue of (L/D)/(Px/Py) was in a range from 7 to 8.

Also in the case where the air ejection holes are arranged in 4 rows orlarger even-numbered rows in the resin film carrying direction, the airejection nozzle satisfying the formula (1) can be designed, but in thiscase, since the dimension of the air ejection nozzle in the resin filmcarrying direction becomes large, the flow of air into the suction portsin the tenter oven is inhibited while the dimension of the tenter ovenin the resin film carrying direction becomes large. Therefore, such anair ejection nozzle has problems in view of practicality.

Next, the formula (2) is explained below. Based on the numerous studiesconcerning free jet and impact jet, it is well known that the structureof a flow field formed by a jet can be expressed by L/D. According tothese studies, when the value of L/D is in a range from 6 to 8, apotential region where the air velocity at the center of a jet maintainsan initial air velocity exists, but if the value of L/D is larger than10, the turbulence of the jet perfectly develops. If the turbulence of ajet develops, velocity variation becomes large to destabilize the jet,and a pressure difference and pressure variation may exist around thejet. In this case, the flow field is likely to be disturbed. Thepotential core region is strong in the capability to flow rectilinearlyand is unlikely to be disturbed by pressure difference or pressurevariation. Therefore, it is preferred that the value of L/D is 8 orless, and more preferred is 6 or less.

Further, it is known that a jet more apart from its air ejection holeentrains the surrounding air more, to spread the mixing region in theradial direction of the air ejection hole. If the value of L/D is toosmall, the spread of the mixing region is insufficient, and the jetcolliding with the surface of the resin film is like a spot, notallowing the effect explained for the formula (1) to be obtained.Therefore, it is preferred that the value of L/D is 4 or more. As aresult of discussion performed by using the method shown in theexamples, it was confirmed that an L/D value of 5 or more is morepreferred. Therefore, it is preferred that the value of L/D is 4 to 8. Arange from 5 to 8 is more preferred, and a range from 5 to 6 is furthermore preferred.

Further, in the air ejection nozzle of the invention, if B=2π(D/2)²/Py(where π is the ratio of the circumference of a circle to its diameter),then it is preferred that the following formula (3) is satisfied.12≦L/B≦30  formula (3)

The formula (3) is explained below. B is a hole clearance per unit widthof the air ejection nozzle. The hole clearance per unit width refers toa clearance of a rectangular air ejection hole (slit) in the case wherethe air ejection holes 2 circular in cross sectional form are convertedinto the rectangular air ejection hole (slit) continuous in the widthdirection of the resin film and having an opening area equal to that ofthe circular air ejection holes 2. If the value of B is too small forthe value of L, the heat transfer efficiency may decline as the case maybe. The air ejection velocity (air velocity) of the air ejection nozzleused in a tenter oven depends on the thickness and carrying speed of theresin film, but it is preferred that the air ejection velocity is set ina range from 5 to 35 m/s.

The air velocity can be set in a wide range. At an air ejection velocityof 20 m/s, it is preferred that the heat transfer efficiency of the airejection nozzle is 55 W/(m²K) or more. For this purpose, it is preferredthat the value of L/B is 30 or less, and 24 or less is more preferred.Further, if the value of B is too large for the value of L, the amountof circulated air increases to require a heat exchanger and a fanrespectively larger in capacity, thus raising the equipment cost and thepower cost. Therefore, it is preferred that the value of L/B is 12 ormore, and 15 or more is more preferred.

The value of L is not especially limited, but it is preferred that thevalue of L is in the range of 140 mm to 270 mm. If the value of L isless than 140 mm, it may be difficult to secure the space in which theclips used for carrying the resin film pass. If the value of L is morethan 270 mm, a heat exchanger and a fan respectively large in capacityare required for obtaining the necessary heat transfer efficiency, toraise the equipment cost and the power cost.

The value of D is not especially limited either. However, in view of theabovementioned preferred ranges of L/D and L, it is preferred that thevalue of D is in the range of L/8 to L/5, and in the range of L/6 to L/5is more preferred.

The value of Px is not especially limited, but it is preferred that thevalue of Px is in the range of 50 mm to 180 mm. In the range of 70 mm to150 mm is more preferred. If the value of Px is too small, being lessthan 50 mm, the jets of the air ejection holes adjacent to each otherinterfere with each other and may be bent or shaken. If the value of Pxis too large, being more than 180 mm, the dimension of the air ejectionnozzle in the resin film carrying direction becomes large. Therefore,the flow into the suction ports is inhibited, and the dimension of thetenter oven in the resin film carrying direction may become large. It ispreferred that the value of Px is in the range of 50 mm to 180 mm.

The value of Py is not especially limited, but it is preferred that thevalue of Py is in the range of 50 mm to 200 mm. A more preferred rangeis 70 mm to 180 mm. If the Py value is too small, being less than 50 mm,the jets of the air ejection holes adjacent to each other may interferewith each other and may be bent or shaken. If the Py value is too large,being more than 200 mm, the jets colliding with the surface of the resinfilm are like spots, not allowing the effect explained for the formula(1) to be obtained as the case may be. Therefore, it is preferred thatthe Py value is in the range of 50 mm to 200 mm.

The resin film to be heat-treated by the air ejection nozzle or thetenter oven of the invention is not especially limited. The resin filmcan be, for example, a polyester film, polypropylene film, polyamidefilm, polylactic acid film, polyolefin film or polyphenylene sulfidefilm.

The tenter oven of the invention in which the air ejection nozzle of theinvention is installed at least in any one of the zones of a preheatingzone, stretching zone, heat setting zone and cooling zone preferablyallows the production of any of the abovementioned various films uniformin heat treatment effect, especially uniform in the heat treatmenteffect in the width direction.

In the tenter oven of the invention, it is preferred that the airejection nozzle of the invention is installed at least in the preheatingzone. Further, it is more preferred that the air ejection nozzle of theinvention is installed not only in the preheating zone but also in anyone zone of the stretching zone, heat setting zone and cooling zone. Itis further more preferred that the air ejection nozzle of the inventionis installed in all the zones of the preheating zone, stretching zone,heat setting zone and cooling zone.

The air ejection nozzle and tenter oven of the invention are explainedbelow on the basis of examples.

The example of the heat transfer rate distribution 33 on the surface ofa resin film 31 shown in FIG. 3 was obtained by three-dimensionalcomputational fluid analysis. FIG. 8 is a sectional view of the analysismodel of a tenter oven 51 used in the examples of the invention, showingthe plane perpendicular to the surface of a resin film 31 including thecarrying direction FTD of the resin film 31. This analysis model drawingshows the upper half of a vertical structure symmetric with respect tothe plane of the resin film 31.

In FIG. 8, with regard to the size of the tenter oven 51, the length ofthe tenter oven 51 in the carrying direction FTD of the resin film 31was 2 m, and the length of the tenter oven 51 in the width direction ofthe resin film 31 was 2 m, and the height of the tenter oven 51 from theresin film 31 to the upper inner wall face of the tenter oven 51 was(L/1,000+1) m, where L is the distance between the air ejection face andthe passing plane of the resin film defined before.

The outside spaces 61 of the tenter oven 51 were added in order that theend boundaries 62 of the analysis space do not affect the flow field inthe tenter oven 51, and do not affect the constitution of the tenteroven 51. The end boundaries 62 of the analysis space are pressureboundaries, and as the boundary condition, atmospheric pressure (0.1MPa) was set. With regard to the size of the outside spaces 61, thelength of the outside spaces 61 in the carrying direction FTD of theresin film 31 was 1 m, and the length of the outside spaces 61 in thewidth direction of the resin film 31 was 2 m equal to the length (width)2 m (not shown in the drawing) of the tenter oven 51 in the directionperpendicular to the carrying direction FTD of the resin film 31, andthe height of the outside spaces 61 was (L/1,000+1) m equal to theheight of the tenter oven 51.

The resin film 31 was modeled as a wall boundary moving at a speed of 1m/s. The length of the resin film 31 in the width direction was 1 m, andthe center of the resin film 31 in the width direction was positioned atthe center of the tenter oven 51 in the width direction. That is, thecenter of the tenter oven 51 in the width direction of the resin film 31is made to agree with the center of the resin film 31 in the widthdirection. Further, since the resin film 31 was carried continuously inthe carrying direction FTD, the resin film 31 was positioned to becontinuous from one end to the other end of the analysis model.

The tenter oven 51 was constituted such that five air ejection nozzles 1were disposed on the side above the resin film 31.

With regard to the size of the air ejection nozzles 1, the length ofeach air ejection nozzle 1 in the carrying direction of the resin film31 was 200 mm, and the length of each air ejection nozzle 1 in the widthdirection of the resin film was 1,400 mm, and the height of each airejection nozzle 1 was 600 mm, and the center of each air ejection nozzle1 in the direction perpendicular to the carrying direction FTD of theresin film 31 was positioned at the center of the tenter oven 51 in thewidth direction. That is, the center of the tenter oven 51 in the widthdirection of the resin film 31 is made to agree with the center of eachair ejection nozzle 1 in the width direction of the resin film 31.

Further, among the five air ejection nozzles 1, the air ejection nozzle1 positioned at the center (the third air ejection nozzle 1 on theupstream side in the carrying direction of the resin film 31) waspositioned at the center of the tenter oven 51 in the carryingdirection. That is, the center of the air ejection nozzle 1 positionedat the center in the carrying direction FTD of the resin film 31 is madeto agree with the center of the tenter oven 51 in the carrying directionFTD of the resin film 31. Further, each interval Pn between the centerlines between the air ejection nozzles 1 adjacent to each other in thecarrying direction of the resin film 31 was 300 mm. Therefore, everyinterval between the respectively adjacent air ejection nozzles 1 is 100mm.

In the faces of the air ejection nozzles 1 facing the resin film 31 (airejection faces 40A), many circular air ejection holes 2 having diameterD (mm) were provided. The distance between the passing plane FPf of theresin film 31 and the air ejection faces 40A was L (mm). The airejection holes 2 were modeled as an inflow boundary, and as the boundarycondition, an air flow velocity of 20 m/s was set.

The air ejection holes 2 were arranged, as shown in FIG. 1, in two rowsof first row 2 a and second row 2 b in the direction perpendicular tothe carrying direction FTD of the resin film 31, and the air ejectionholes 2 of the first row 2 a and the air ejection holes 2 of the secondrow 2 b were arranged zigzag in the plan view. The interval between thestraight line 3 a (the first air ejection holes-aligned straight line)passing through the centers of the air ejection holes 2 arranged in thefirst row 2 a extending in the width direction of the resin film 31 andthe straight line 3 b (the second air ejection holes-aligned straightline) passing through the centers of the air ejection holes 2 arrangedin the second row 2 b extending in the width direction of the resin film31 was expressed as Px (mm), and each interval between the centers ofthe air ejection holes 2 adjacent to each other in each row in the widthdirection of the resin film 31 was expressed as Py (mm).

The suction port 54A was modeled as an outflow boundary, and as theboundary condition, an outflow amount equal to the inflow amount fromall the air ejection holes 2 was set. With regard to the size of thesuction port 54A, the length of the suction port 54A in the carryingdirection FTD of the resin film 31 was 1,400 mm, and the length of thesuction port 54A in the width direction of the resin film 31 was 1,400mm, and the suction port 54A was disposed above the air ejection nozzles1. The distance between the suction port 54A and the faces (top faces)of the air ejection nozzles 1 opposite to the air ejection faces 40A was100 mm. The height of the suction duct 54 provided with the suction port54A was 200 mm, and the face as a whole of the suction duct 54 facingthe air ejection nozzles 1 was formed as the suction port 54A. Further,the suction port 54A was disposed at the center in the width directionof the tenter oven 51 and the center in the carrying direction FTD ofthe resin film 31. That is, the center of the suction port 54A in thewidth direction of the resin film 31 is made to agree with the center ofthe tenter oven 51 in the width direction of the resin film 31, and thecenter of the suction port 54A in the carrying direction FTD of theresin film 31 is made to agree with the center of the tenter oven 51 inthe carrying direction FTD of the resin film 31.

With regard to the physical properties of the fluid, dry air ofatmospheric pressure at a temperature of 100° C. was assumed to have adensity of 0.93 kg/m³, a viscosity of 2.2×10⁻⁵ Pa's, a specific heat of1,012 J/(kg·K) and a heat conductivity of 0.031 W/(m·K).

For analysis, commercially available general purpose hot fluid analysissoftware, “STAR-CD (produced by CD-adapco Japan Co., Ltd.) was used toperform steady calculation. For handling turbulent flow, a k-ε turbulentflow model was used, and for handling a turbulent flow boundary layernear a wall, a wall law was used.

The abovementioned software is intended to analyze the Navier-StokesEquation as a fluid motion equation by a finite volume method. Ofcourse, any other hot fluid analysis software can also be used ifsimilar analysis can be performed.

The heat transfer efficiency refers to the mean value of the heattransfer rates which the resin film 31 receives when it passes the airejection nozzles 1. That is, the heat transfer efficiency of one airejection nozzle 1 is the mean value in the carrying direction FTD of theresin film 31, of the heat transfer rates of the surface of the resinfilm 31 in the section Pn between the center line 4 a with the adjacentair ejection nozzle 11 a and the center line 4 b with the adjacent airejection nozzle 11 b. Since the five air ejection nozzles installed sideby side in the carrying direction FTD of the resin film 31 wereidentical in the arrangement of the air ejection holes 2, the heattransfer efficiency was calculated with the central one air ejectionnozzle 1 as a representative of the respective air ejection nozzles.

Example 1

With L=150 mm, D=25 mm, Px=100 mm and Py=122 mm, the abovementionedanalysis was performed. FIG. 9 is a chart showing the state of the heattransfer efficiency distribution of the air ejection nozzle 1 in thewidth direction of the film 31. In the chart, the position P (in mm) inthe width direction of the resin film 31 is chosen as the abscissa, andthe heat transfer efficiency Q (in W/m²K) of the air ejection nozzle 1,as the ordinate. This chart was used to evaluate the following twoitems.

(1) Average heat transfer efficiency Qa of air ejection nozzle 1:

The mean value of the heat transfer efficiency values of the airejection nozzle 1 distributed in the width direction of the resin film31 is defined as the average heat transfer efficiency Qa (in W/m²K) ofthe air ejection nozzle 1. It is preferred that the average heattransfer efficiency Qa is larger. In the invention, like the indicatorof a general tenter oven, it was evaluated that the object of theinvention was achieved and that the air ejection nozzle was acceptablein the case where the value of the average heat transfer efficiency Qawas 55 W/m²K or more.

(2) Heat transfer efficiency irregularity Rq of air ejection nozzle 1 inthe width direction of resin film 31:

The value obtained by dividing the difference between the maximum valueQmax and the minimum value Qmin of the heat transfer efficiency Q of theair injection nozzle 1 in the width direction of the resin film 31 bythe average heat transfer efficiency Qa and multiplying the quotient by100 was defined as the heat transfer efficiency irregularity Rq (in %)of the air ejection nozzle 1 in the width direction of the resin film31. In FIG. 9, the maximum value of heat transfer efficiency Q isindicated by dotted line Qmax, the minimum value of heat transferefficiency Q, by dotted line Qmin, and the mean value of heat transferefficiency Q (average heat transfer efficiency Qa), by solid line Qa. Itis preferred that the heat transfer efficiency irregularity Rq issmaller. In the invention, since the heat transfer efficiencyirregularity Rq of a general slit nozzle is 5 to 15%, it was evaluatedthat the object of the invention was achieved and that the air ejectionnozzle was acceptable in the case where the value of the heat transferefficiency irregularity Rq was 15% or less.

The evaluation results of Example 1 were Qa=72.0 W/m²K and Rq=10.9%,showing that both the average heat transfer efficiency Qa and the heattransfer efficiency irregularity Rq were acceptable.

Examples 2 to 15 and Comparative Examples 1 to 13

L, D, Px and Py were changed with the value of L/D kept in a range from5 to 8, to perform the abovementioned analysis as described forExample 1. The values of L, D, Px and Py used for analysis and thevalues of average heat transfer efficiency Qa and the values of heattransfer efficiency irregularity Rq evaluated are shown in Table 1.

In Examples 2 to 15 in which the value of (L/D)/(Px/Py) was kept in arange from 6 to 9, the values of average heat transfer efficiency Qawere 55 W/m²K or more and the values of heat transfer efficiencyirregularity Rq were 15% or less, showing that the results of therespective examples were acceptable.

In Comparative Examples 1 to 13 in which the value of (L/D)/(Px/Py) wassmaller than 6 or larger than 9, the values of average heat transferefficiency Qa were 55 W/m²K or more, but the values of heat transferefficiency irregularity Rq were larger than 15%, showing that theresults of the respective comparative examples were not acceptable,namely, were rejected.

Comparative Examples 14 to 17

With L=270 mm, D=30 mm and Py=88 mm, the value of Px was changed in arange from 80 to 140 mm, to perform the abovementioned analysis asdescribed for Example 1. The values of L, D, Px and Py used foranalysis, and the values of average heat transfer efficiency Qa and thevalues of heat transfer efficiency irregularity Rq evaluated are shownin Table 1.

In Comparative Examples 14 to 17 in which the value of L/D was 9, thevalues of average heat transfer efficiency Qa were 55 W/m²K or more, butthe values of heat transfer efficiency irregularity Rq were larger than15%, showing that the respective comparative examples were notacceptable, namely, were rejected.

TABLE 1 L D Px Py B (L/D)/ Qa Rq [mm] [mm] [mm] [mm] [mm] L/B L/D Px/Py(Px/Py) [W/m²K] [%] Comparative 150 25 80 122 8.0 18.6 6.0 0.7 9.2 69.618.3 example 1 Example 1 150 25 100 122 8.0 18.6 6.0 0.8 7.3 72.0 10.9Example 2 150 25 120 122 8.0 18.6 6.0 1.0 6.1 71.3 13.3 Comparative 15025 140 122 8.0 18.6 6.0 1.1 5.2 69.0 23.1 example 2 Comparative 150 3080 176 8.0 18.7 5.0 0.5 11.0 69.8 22.2 example 3 Example 3 150 30 100176 8.0 18.7 5.0 0.6 8.8 72.9 9.5 Example 4 150 30 120 176 8.0 18.7 5.00.7 7.3 74.3 7.1 Example 5 150 30 140 176 8.0 18.7 5.0 0.8 6.3 73.5 10.0Comparative 180 25 80 108 9.1 19.8 7.2 0.7 9.7 66.7 20.7 example 4Example 6 180 25 100 108 9.1 19.8 7.2 0.9 7.8 69.6 12.4 Example 7 180 25120 108 9.1 19.8 7.2 1.1 6.5 69.1 14.1 Comparative 180 25 140 108 9.119.8 7.2 1.3 5.6 66.5 17.6 example 5 Comparative 180 30 80 156 9.1 19.96.0 0.5 11.7 65.9 23.6 example 6 Comparative 180 30 100 156 9.1 19.9 6.00.6 9.4 69.8 16.8 example 7 Example 8 180 30 120 156 9.1 19.9 6.0 0.87.8 71.4 9.4 Example 9 180 30 140 156 9.1 19.9 6.0 0.9 6.7 71.0 10.0Comparative 240 30 80 100 14.1 17.0 8.0 0.8 10.0 65.1 24.8 example 8Example 10 240 30 100 100 14.1 17.0 8.0 1.0 8.0 69.2 11.3 Example 11 24030 120 100 14.1 17.0 8.0 1.2 6.7 69.4 11.9 Comparative 240 30 140 10014.1 17.0 8.0 1.4 5.7 67.6 21.0 example 9 Comparative 240 35 80 136 14.117.0 6.9 0.6 11.7 66.9 26.3 example 10 Comparative 240 35 100 136 14.117.0 6.9 0.7 9.3 67.5 17.7 example 11 Example 12 240 35 120 136 14.117.0 6.9 0.9 7.8 71.9 7.4 Example 13 240 35 140 136 14.1 17.0 6.9 1.06.7 71.8 8.2 Comparative 270 30 80 88 16.1 16.8 9.0 0.9 9.9 61.5 19.5example 14 Comparative 270 30 100 88 16.1 16.8 9.0 1.1 7.9 59.7 21.1example 15 Comparative 270 30 120 88 16.1 16.8 9.0 1.4 6.6 61.8 19.1example 16 Comparative 270 30 140 88 16.1 16.8 9.0 1.6 5.7 59.7 22.1example 17 Comparative 270 35 80 120 16.0 16.8 7.7 0.7 11.6 65.8 25.2example 12 Comparative 270 35 100 120 16.0 16.8 7.7 0.8 9.3 66.9 15.6example 13 Example 14 270 35 120 120 16.0 16.8 7.7 1.0 7.7 70.2 11.7Example 15 270 35 140 120 16.0 16.8 7.7 1.2 6.6 69.9 12.5

FIG. 10 is a graph in which the values of (L/D)/(Px/Py) used and thevalues of heat transfer efficiency irregularity Rq obtained in Examples1 to 15 and Comparative Examples 1 to 17 are plotted. In the graph ofFIG. 10, the value of (L/D)/(Px/Py) is chosen as the abscissa, and thevalue of heat transfer efficiency irregularity Rq (%), as the ordinate.Circles indicate the values of Examples 1 to 15, triangles, the valuesof Comparative Examples 1 to 13, and crosses, the values of ComparativeExamples 14 to 17.

From the graph of FIG. 10, it can be seen that as the value of(L/D)/(Px/Py) becomes smaller than 6, the value of heat transferefficiency irregularity Rq becomes suddenly large. Further, it can beseen that as the value of (L/D)/(Px/Py) becomes larger than 9, the valueof heat transfer efficiency irregularity Rq becomes suddenly large.Furthermore in Comparative Examples 14 to 17 where the value of L/D is9, it can be seen that even though the value of (L/D)/(Px/Py) is kept ina range from 6 to 9, the value of heat transfer efficiency irregularityRq does not become small.

FIG. 11 is a graph in which the values of Px/Py and the values of L/D inExamples 1 to 15 and Comparative Examples 1 to 17 are plotted. In thegraph of FIG. 11, the value of Px/Py is chosen as the abscissa, and thevalue of L/D, as the ordinate. Circles indicate the values of Examples 1to 15, triangles, the values of Comparative Examples 1 to 13, andcrosses, the values of Comparative Examples 14 to 17. Further, dottedline L6 indicates the line of (L/D)/(Px/Py)=6, dotted line L9, line of(L/D)/(Px/Py)=9, and dotted line L8, line of L/D=8.

From the graph of FIG. 11, it can be seen that in Examples 1 to 15 inwhich the values of heat transfer efficiency irregularity Rq are small,the values of (L/D)/(Px/Py) are kept in a range from 6 to 9 while thevalues of L/D are kept in a range from 5 to 8.

Example 16

An air ejection nozzle 1 having the same dimensions as those of Example1 was installed in the preheating zone of the tenter apparatus 95 shownin FIG. 4, and the production process shown in FIG. 7 was used toproduce a biaxially oriented polyethylene terephthalate resin film 31 d.

Production Conditions:

Chips of polyethylene terephthalate dried in vacuum at a temperature of180° C. were supplied into the extruder 91, and the resin melted at atemperature of 280° C. was extruded, being discharged as a sheet fromthe die 92, to obtain a resin sheet 31 a. The resin sheet 31 a was woundaround the casting drum 93 with a surface temperature of 20° C., to becooled and solidified, for obtaining a cast film 31 b. In succession,the cast film 31 b was introduced into the longitudinal stretchingmachine 94, heated by rolls heated to a temperature of 80° C., furtherstretched to 3.2 times in the carrying direction while being heated byan infrared heater, and cooled by a cooling roll with a temperature of40° C., to obtain a monoaxially oriented film 31 c. In succession, themonoaxially oriented film 31 c was introduced into the tenter apparatus95, heated to a temperature of 100° C. in the preheating zone, stretchedto 3.5 times in the width direction while being heated to a temperatureof 110° C. in the stretching zone, heated to a temperature of 220° C. inthe heat setting zone, and cooled to a temperature of 90° C. in thecooling zone while being treated for relaxation by 5% in the widthdirection, to obtain a biaxially oriented film 31 d. Then, both theedges of the biaxially stretched film 31 d were off, and the film waswound around the winding roll 96, to obtain a film 31 e having a widthof 3,400 mm as a product.

Thickness Measuring Method:

From the film 31 e wound as a product around the winding roll 96, asample having a size of 3,400 nm in the width direction and 30 mm in thecarrying direction was obtained by cutting, and the thickness values ofthe sample film distributed in the width direction were measured usingFilm Thickness Tester “KG601A” and Electronic Micrometer “K306C”respectively produced by Anritsu K.K. The thickness irregularity Rt (in%) in the width direction was obtained from relational expressionRt=(Tx−Tn)/Ta×100 [%], wherein Ta is the mean thickness value (in μm);Tn, the minimum thickness value (in μm); and Tx, the maximum thicknessvalue (in μm).

The thickness values distributed in the width direction of the film 31 eas a product of Example 16 are shown in the graph of FIG. 12. In thegraph of FIG. 12, the position (mm) in the width direction is chosen asthe abscissa, and the thickness value, as the ordinate. Solid line Taindicates the mean thickness value, dotted line Tx, the maximumthickness value, and dotted line Tn, the minimum thickness value. Theresults of Example 16 were Ta=74.9 μm, Tn=74.3 μm, Tx=75.5 μm andRt=1.6%.

Comparative Example 18

An air ejection nozzle 1 having the same dimensions as those ofComparative Example 1 was installed in the preheating zone of the tenterapparatus 95 shown in FIG. 4, and a biaxially stretched polyethyleneterephthalate resin film 31 d (film 31 e as a product) was producedunder the same conditions as described for Example 16. The thicknessvalues were measured according to the same method as that of Example 16.

The thickness values distributed in the width direction of the film 31 eas the product of Comparative Example 18 are shown in the graph of FIG.13. In the graph of FIG. 13, the position (mm) in the width direction ischosen as the abscissa, and the thickness value, as the ordinate. Solidline Ta indicates the mean thickness value, dotted line Tx, the maximumthickness value, and dotted line Tn, the minimum thickness value. Theresults of Comparative Example 18 were Ta=75.1 μm. Tn=74.1 μm, Tx=76.0μm and Rt=2.5%.

If the heat transfer efficiency irregularity Rq of the air ejectionnozzle 1 is large, the temperature irregularity of the resin film 31after passing through the preheating zone becomes large, to causestretching irregularity in the stretching zone, thus enlarging thethickness irregularity Rt in the width direction. Since the value ofheat transfer efficiency irregularity Rq in Example 16 is very smallerthan the value of the heat transfer efficiency irregularity Rq inComparative Example 18, the air ejection nozzle 1 of Example 16 is goodin the uniformity of heat transfer efficiency in the width direction ofthe resin film.

INDUSTRIAL APPLICABILITY

Since the air ejection nozzle of the invention has specifically formedmany air ejection holes arranged in a specific relationship, the resinfilm heat-treated using the air ejection nozzle is excellently uniformin the heat transfer efficiency in the width direction of the resinfilm. Therefore, the tenter oven of the invention using the air ejectionnozzle of the invention allows the production of a resin film havinghomogeneous heat-treated properties in the width direction. The airejection nozzle of the invention can be used not only for a tenter ovenbut also as a drying device used in a printing machine or coatingmachine, etc.

1. (a) An air ejection nozzle which is provided against a passing planeof a resin film being carried in one direction with a clearance and usedfor ejecting air toward a surface of the resin film, wherein (b) the airejection nozzle comprises a nozzle housing, and the nozzle housing hasan air supply passage therein, an air ejection face facing the passingplane of the resin film, and many air ejection holes opening to the airsupply passage and opening in the air ejection face respectively, (c)the many air ejection holes in the air ejection face are circular, (d)the many air ejection holes are arranged in the air ejection face in tworows including a first row and a second row in the directionperpendicular to the carrying direction of the resin film, with the airejection holes of the first row and the air ejection holes of the secondrow being arranged in a zigzag arrangement, and (e) the distance L (mm)between the air ejection face and the passing plane of the resin film,the diameter D (mm) of the respective air ejection holes in the airejection face, the interval Px (mm) in the carrying direction of theresin film between first air ejection holes aligned in a straight linepassing through the centers of the multiple air ejection holes arrangedin the first row and a second air ejection holes aligned in a straightline passing through the centers of the multiple air ejection holesarranged in the second row, and each interval Py (mm) between thecenters of the respectively adjacent air ejection holes in the first airejection hole aligned straight line and between the centers of therespectively adjacent air ejection holes in the second air ejection holealigned straight line satisfy the following formulae (1) and (2):6≦(L/D)/(Px/Py)≦9  formula (1)4≦L/D≦8  formula (2).
 2. The air ejection nozzle according to claim 1,wherein the following formula (3) is satisfied:12≦L/B≦30  formula (3) wherein B=2π(D/2)²/Py (wherein π is the ratio ofthe circumference of a circle to its diameter).
 3. The air ejectionnozzle according to claim 1, wherein the distance L is 140 to 270 mm.